1. Field of the Invention
The present invention relates to a printing system and a printing control method, and more particularly to a printing system and a method of controlling the printing system which is constituted by an information processing apparatus such as a personal computer and a printing apparatus such as a printer and performs printing associated with a calibration.
2. Description of the Related Art
A printing apparatus (also referred to simply as a printer) is widely used as an apparatus for outputting image information in an information processing system. As one such printing apparatus an electrophotographic printer using a laser beam forms a visible image by fixing a toner onto a sheet of paper. An ink jet printer of a bubble jet type, for example, ejects ink onto the sheet to form a visible image. A printing process or printing mechanism of such printers is becoming more and more complicated because of a growing trend in recent years for higher resolution and color printing required of the printer.
Such printers, due to an environmental change and wear of parts, may vary its electric or mechanical quality showing upon forming a visible image, differentiating the visible image formed. Typical examples of image variation include, for example, a change in density or a gradation of the density of a printed image or a change in a tone of a color image.
To cope with a quality degradation of a visible image in printing an image, correction processing is made for image processing functions, such as a .gamma. correction table, that determine a relation between input and output images. This correction is generally called a calibration.
The calibration for the .gamma. correction table, for example, is carried out as follows. Input data of a plurality of values of density or gradation levels is entered into a printer to be calibrated and a predetermined image such as a patch pattern is printed. Then, the density of the printed image is measured to obtain actual density values corresponding to the plurality of input density values (also referred to as "calibration information" herein after). Next, ratios of the actual density values to the input density values are made content of the .gamma. correction table to update the correction values, thus completing the calibration of the .gamma. correction table.
Known examples of the calibration executed in a print system constituted by a host device such as a personal computer (also referred to simply as a host) and a printer are as follows.
In a first example, where the host supplies print data in a form of a print job described with a page description language (PDL) to the printer, the host does not perform the calibration but instead the printer performs the calibration. More specifically, a controller of the printer accepts a calibration request from an engine of the printer at a predetermined timing and updates a correction table so that the calibration can be performed on a printer side. Then, when the printer receives the print job, the controller corrects the image data (print job) by using the updated correction table.
In a second example, where the host supplies print data in a form of a binary print job to the printer, the host is connected to the printer through a two-way communication channel and gets the calibration information from the printer, Based on the gotten calibration information, the host generates a new correction table so that the calibration is performed. The host then generates image data (print job) corrected by the new correction table. Also in this example, the calibration information is generated on the printer side. That is, in response to a request issued from the printer engine at a predetermined timing, the printer controller generates the calibration information.
However, in either of the above examples, carrying out the calibration requires the printer to perform printing and measuring operations for generating the calibration information. During the printing and measuring operations for the calibration, a usual printing operation cannot be performed. More specifically, the printer controller is so configured that, when the controller receives a request for the calibration from the printer engine at time when the controller begins to control printing based on the transferred print job from the host or while the controller is controlling printing of the print job, the controller does not begin to carry out or interrupts the usual printing and generates the calibration information.
On the other hand, when monochromatic image, particularly a document, is to be printed, the density change usually may not pose any critical problem in terms of image quality. Or a user of the printing system sometimes may want a printed result quickly without regard to the print quality. Executing the calibration, particularly generating the calibration information among others, in the case that the calibration is not absolutely needed to be performed, unnecessarily prolongs the time it takes to obtain the printed result. Further, such a printing system cannot be said to be the one that appropriately deals with the requirements of the user.